control-flow-abstraction-generator

# Control Flow Abstraction Generator

Generate abstract Control Flow Graph representations of programs.

## Overview

This skill analyzes program code and generates Control Flow Graphs (CFGs) that abstract the program's control flow structure. CFGs show how execution flows through the program via nodes (statements, conditions) and edges (control transfers), making them suitable for static analysis, formal verification, and program understanding.

## How to Use

Provide:
1. **Program code**: Function or program to analyze
2. **Analysis scope**: Function-level or program-level
3. **Output format** (optional): Textual, DOT, JSON, or multiple

The skill will generate:
- CFG with nodes and edges
- Node types (entry, exit, statement, condition, merge)
- Edge types (sequential, true/false branches, back edges, calls)
- Optional: DOT format for visualization, JSON for tool integration

## CFG Generation Workflow

### Step 1: Parse Program Structure

Identify program constructs:
- **Sequential statements**: Assignments, expressions, declarations
- **Conditional statements**: if-then-else, switch-case
- **Loop statements**: while, for, do-while
- **Function calls**: Direct calls, recursive calls
- **Control transfers**: break, continue, return, goto
- **Exception handling**: try-catch-finally

### Step 2: Create CFG Nodes

Generate nodes for each construct:

**Entry Node**: Function/program start
- Label: `ENTRY` or function name
- Type: `entry`
- Successors: First statement

**Exit Node**: Function/program end
- Label: `EXIT` or `return`
- Type: `exit`
- Predecessors: All return points

**Statement Node**: Regular statement
- Label: Statement text or line number
- Type: `statement`
- Represents: Assignment, call, expression

**Condition Node**: Branch decision
- Label: Boolean expression
- Type: `condition`
- Successors: True branch, false branch

**Merge Node**: Branch join point
- Label: `MERGE` or empty
- Type: `merge`
- Predecessors: Multiple branches

### Step 3: Create CFG Edges

Connect nodes with appropriate edges:

**Sequential Edge**: Normal flow
- From: Statement/node
- To: Next statement/node
- Label: None or `→`

**True Edge**: Condition true branch
- From: Condition node
- To: True branch first statement
- Label: `T` or `true`

**False Edge**: Condition false branch
- From: Condition node
- To: False branch first statement
- Label: `F` or `false`

**Back Edge**: Loop iteration
- From: Loop body end
- To: Loop header
- Label: `↶` or `back`

**Call Edge**: Function invocation (interprocedural)
- From: Call site
- To: Called function entry
- Label: `⇒` or `call`

**Return Edge**: Function return (interprocedural)
- From: Called function exit
- To: Call site return point
- Label: `⇐` or `return`

### Step 4: Handle Special Constructs

**Loops**: Create back edges from body to header

**Break**: Create edge from break statement to loop exit

**Continue**: Create back edge from continue to loop header

**Return**: Create edge from return to EXIT node

**Exceptions**: Create exception edges from try block to catch handlers

### Step 5: Generate Output

Produce CFG in requested format(s):
- Textual representation
- DOT format for Graphviz
- JSON for tool integration

## Example: Simple Conditional

**Code**:
```python
def max_value(x, y):
    if x > y:
        result = x
    else:
        result = y
    return result
```

**CFG (Textual)**:
```
Node 1 (ENTRY):
  Label: max_value
  Successors: [2]

Node 2 (x > y):
  Type: condition
  Predecessors: [1]
  Successors: [3 (true), 4 (false)]

Node 3 (result = x):
  Type: statement
  Predecessors: [2]
  Successors: [5]

Node 4 (result = y):
  Type: statement
  Predecessors: [2]
  Successors: [5]

Node 5 (MERGE):
  Type: merge
  Predecessors: [3, 4]
  Successors: [6]

Node 6 (return result):
  Type: statement
  Predecessors: [5]
  Successors: [7]

Node 7 (EXIT):
  Predecessors: [6]
```

**CFG (Visual)**:
```
    ENTRY
      ↓
   [x > y]
    ↓   ↓
   T↓   ↓F
    ↓   ↓
[result=x] [result=y]
    ↓       ↓
    └→MERGE←┘
        ↓
  [return result]
        ↓
      EXIT
```

**CFG (DOT)**:
```dot
digraph CFG {
  node [shape=box];

  n1 [label="ENTRY", shape=ellipse];
  n2 [label="x > y", shape=diamond];
  n3 [label="result = x"];
  n4 [label="result = y"];
  n5 [label="MERGE", shape=circle];
  n6 [label="return result"];
  n7 [label="EXIT", shape=ellipse];

  n1 -> n2;
  n2 -> n3 [label="T", color=green];
  n2 -> n4 [label="F", color=red];
  n3 -> n5;
  n4 -> n5;
  n5 -> n6;
  n6 -> n7;
}
```

## Example: While Loop

**Code**:
```python
def sum_to_n(n):
    sum = 0
    i = 0
    while i < n:
        sum += i
        i += 1
    return sum
```

**CFG (Visual)**:
```
    ENTRY
      ↓
   [sum = 0]
      ↓
   [i = 0]
      ↓
      ┌─────────┐
      ↓         ↑
   [i < n]      ↑ (back edge)
    ↓   ↓       ↑
   T↓   ↓F      ↑
    ↓   ↓       ↑
[sum += i]      ↑
      ↓         ↑
  [i += 1]──────┘
      ↓F
[return sum]
      ↓
    EXIT
```

**Key Features**:
- Loop header: `[i < n]`
- Back edge: From `[i += 1]` to `[i < n]`
- Exit edge: False branch from condition to return

**CFG (Textual)**:
```
Node 1 (ENTRY)
  → Node 2

Node 2 (sum = 0)
  → Node 3

Node 3 (i = 0)
  → Node 4

Node 4 (i < n) [LOOP HEADER]
  →T Node 5
  →F Node 7

Node 5 (sum += i)
  → Node 6

Node 6 (i += 1)
  → Node 4 [BACK EDGE]

Node 7 (return sum)
  → Node 8

Node 8 (EXIT)
```

## Example: Nested Control Flow

**Code**:
```python
def process(arr, threshold):
    result = []
    for item in arr:
        if item > threshold:
            result.append(item * 2)
        else:
            if item < 0:
                continue
            result.append(item)
    return result
```

**CFG (Visual)**:
```
ENTRY
  ↓
[result = []]
  ↓
[i = 0]
  ↓
  ┌──────────────────────┐
  ↓                      ↑
[i < len(arr)]           ↑
  ↓T                     ↑
[item = arr[i]]          ↑
  ↓                      ↑
[item > threshold]       ↑
  ↓T            ↓F       ↑
[result.append  [item<0] ↑
 (item*2)]